1. Field of the Invention
The present invention relates to a liquid discharge apparatus, a printer head, and a method for making the liquid discharge apparatus. The liquid discharge apparatus is applicable to, for example, ink jet printers.
2. Description of the Related Art
A conventional ink jet printer discharges ink droplets through a printer head toward an object such as paper for forming a required image on the object. The printer head discharges the droplets of the ink contained in a liquid chamber through nozzles by a driving element that causes a change in pressure in the liquid chamber. Examples of known driving elements are heating elements and piezoelectric elements.
Such a printer head is fabricated as follows, for example. A driving element integrated with a drive circuit for driving the driving element is formed on a semiconductor substrate by a semiconductor production process, and a photosensitive resin is applied thereon by spin coating. Partition walls of liquid chambers and liquid channels are formed by photolithography of the photosensitive resin. A sheet provided with nozzles (hereinafter referred to as “nozzle sheet”) is formed by electrotyping and is disposed on the substrate.
In this process, the photosensitive resin is maintained at a semicured state. This nozzle sheet is bonded to the top faces of the partitions of the liquid chambers and the liquid channels, and the semicured photosensitive resin is cured by heat for thermocompression bonding of the nozzle sheet. In the present invention, thermocompression bonding from such a semicured state is referred to as “secondary bonding”.
In the secondary bonding, the nozzle sheet must be bonded to the semicured resin. Since the semicured resin contains a reduced number of reactive groups, the bonding strength between the nozzle sheet and the top faces of the partitions is insufficient.
When nickel, which is a typical electrotyping material, is used as a material for the nozzle sheet, the nickel nozzle sheet having poor adhesiveness to resin does not satisfactorily adhere to the top faces of the resin partitions.
In the printer head, ink droplets are discharged from the ink chamber by a change in pressure in the ink chamber as described above. If the nozzle sheet is not sufficiently bonded to the top faces of the partitions, such a change in pressure will cause separation of the nozzle sheet from the partitions. The separation of a nozzle sheet results in undesirable vibration of the nozzle face and of meniscus of other nozzles that do not discharge ink. As a result, this poor adhesion of the nozzle sheet significantly deteriorates the quality of the printed image.
If the bonding strength is extremely low, the shape of the nozzle sheet changes with time, and ink penetrates between the nozzle sheet and the substrate. This penetrated ink damages electrical connections and causes separation of the nozzle sheet in a severe state.